Cocaine and other drugs of abuse have been shown to induce expression of immediate early genes (IEGs), such as c-fos , in the brain. These genes code for transcription factors factors and have been used as markers of neuronal activation, such that the patterns of expression implicate brain areas that may be involved in the neuronal response to a psychoactive drug. Their status as transcription factors suggests that IEGs may mediate some of the behaviors and long-term changes that accompany the use of drugs such as cocaine, although this aspect of IEG activation has not been studied thoroughly. While dopamine systems are thought to be important, evidence has also implicated serotonin (5-HT) systems in the expression of c-Fos in response to cocaine. However, the specific h-HT receptor subtypes involved have not yet been characterized. By utilizing behavioral and molecular techniques, we will obtain a better understanding of the role of c-Fos induction and 5-HT/2A receptors in the behavioral responses elicited by cocaine.